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I have been on vacation for two weeks, leaving my 2023 S206 2.0 L petrol mild hybrid secured in my enclosed yard. Approximately a week later, I received a notification on my phone through the 'My Mercedes' application, indicating ''battery condition critical''. There was little I could do from Switzerland, so I presumed it might be a false alert and that the vehicle was indeed in good condition. Before this, I encountered no issues with the vehicle. I have possessed it for slightly more than a year. I believe a new battery was installed before I acquired it.

Upon arriving home, I attempted to unlock the vehicle. Absolutely nothing! Neither of my two key fobs elicited a response. I successfully opened the passenger door with the 'blade' key. I was unable to open any additional doors or the trunk. The ignition failed to activate. The vehicle was completely devoid of electrical power. I lifted the hood, but lacking a jump starter, I deemed it prudent to contact the RAC. They responded with remarkable promptness (within an hour of being contacted). The proficient RAC technician linked a jump pack to the under-hood terminals and successfully engaged the central locking mechanism to access the trunk. The auxiliary battery in the trunk was entirely depleted. He utilised a fast charger and successfully ignited the engine. The alternator's output was monitored, revealing a robust charge. The battery was noted to charge swiftly, attaining nearly full capacity in approximately 15 minutes. Subsequent observation verified that the charged condition was maintained. The vehicle was turned off and on multiple times, while maintaining the battery charge level. The RAC representative departed, asserting that the battery was likely in good condition and did not necessitate replacement, yet failed to clarify the reason for its depletion within just over a week.

I have utilised the vehicle for a duration of two days. Typical driving tasks - early morning cold starts, completing errands, brief trips, etc. Everything seems satisfactory. I believe the stop-start mechanism is potentially more 'efficient' now than it was previously. The engine now shuts off at traffic signals, whereas it previously remained operational. I am unable to elucidate or comprehend this entirely. I am hesitant to substitute the battery, as I believe it is fairly recent and seems to be functioning adequately at present.

You assert that the stop/start feature operates 'more effectively' than it did prior to the RAC technician recharging the battery.

I propose that if your stop/start function was inconsistent prior to the malfunction but has significantly improved now, the car's batteries were substandard, as the cessation of the stop/start feature typically signifies a deficient starter battery.

I contend that the 2023 S206 2.0 L petrol mild hybrid features a 48v system along with an Integrated Starter Generator (ISG), implying that the 12v battery does not participate in the operation of the engine's starter motor, as this function is managed by the 48v system, nor does it power other significant consumers like the electric power steering and air conditioning compressor.

The 12v battery powers standard components like lighting, infotainment systems, digital dashboards, essential vehicle management control modules—such as door locking—and maintains the car's functionality when idle.

The indicators presented by the original poster imply that the 12v battery was completely depleted. This may result from a malfunctioning 12v battery or a parasitic drain from one or more devices failing to power down appropriately. Given that the vehicle appears to be functioning well with regular use, I would recommend having the diagnostic codes scanned to identify any pertinent issues and also ensuring the 12v battery undergoes a thorough examination.

I lack technical expertise, yet I believed that Standby mode was intended to be enabled on these new w206 models; otherwise, the battery would ultimately be depleted by its various electrical components. It is referenced on page 420 of 1029 in the 2023 owner's manual. Perhaps someone possesses superior knowledge?

I lack technical expertise, yet I believed that Standby mode was intended to be enabled on these new w206 models; otherwise, the battery would ultimately be depleted by its various electrical components. It is referenced on page 420 of 1029 in the 2023 owner's manual. Perhaps someone possesses superior knowledge?

I would commence by following the guidance provided by @MercedesMan98, and subsequently proceed from that point.

I appreciate it. I have inspected my vehicle and it seems that feature is not present.

As recommended by others, I will have the battery examined and proceed based on the findings. I appreciate all those who replied and provided guidance.